SkillsTech

TAFE Queensland SkillsTech is the largest public provider of trade and technician training in Australia in the Automotive, Building and Construction, Electrical and Electronics, Process Control and Instrumentation, Manufacturing, Engineering, Telecoms, CSG/LNG, HDPE and sustainable technologies industries. RTO No. 0275 CRICOS No. 03020E

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Thursday, 3 April 2014

Most
CSG proponents are still operating brown field sites in the Western Downs of
Queensland.Brown field sites are
typified by older reciprocal compressors and hydraulic packs units (HPU’s) that
run on coal seam gas or diesel to drive progressive cavity pumps (PCP’s).These PCP’s bring the coal seam gas and water
to the surface where it is separated. The water is sent to ponds where
desalination and reverse osmosis plants purify the water for agricultural
use.The gas is dried, compressed and
piped to Curtis Island for the LNG (liquefied natural gas) stage.

However,
the newer green field sites use more efficient centrifugal compressors which
require far less maintenance.The PCP
pumps are also changing and moving away from the hydraulic drives to electrical
motors to pump water and gas to the surface.

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Oil Lift Hydraulic Well Head

Hydraulic Packs Unit (HPU) Engine and Head

Until recently, electric induction motors have
been difficult to control. Normally the motors use an on/off or ‘soft start’
control to overcome the initial rush of start-up current which is usually up to
7 times the operating current. These motors characteristically are connected to
the electrical supply grid which is alternating current (AC), 3 phase, 400
volts and 50 hertz frequency.These
direct connect motors are designed for full load and when the load changes or
drops the motor wastes energy and becomes largely inefficient. Enter Variable
Speed/Frequency Drives (VSD’s). Instead of the motor being connected directly
to the supply grid, the VSD is installed between the motor and the grid.

Schneider Electric 15 KW VSD (Variable Speed Drive) Unit

The
VSD unit is connected directly to the grid which is fixed-frequency (50 Hz) and
fixed voltage (400 volt). The unit converts this alternating voltage via an integrated
rectifier to direct current (DC).The
VSD unit contains integrated power electronics and on-board microprocessors (invertors)
which switch this DC on and off rapidly turning the DC back into a controllable
sinusoidal-type output.This new
sinusoidal waveform provides a continuously variable frequency and voltage to
drive the motor.So the fixed sinewave
(50 Hz from the grid) is converted into an infinitely variable controllable
sinewave output. This variable output enables the VSD unit to quickly change
the speed and the torque of the motor in response to the changing load of the
PCP pump, offering improved efficiency.The VSD drives are configured and the parameters are matched to the size
and type of the motor and field based loads. This type of variable control also
extends maintenance cycles and prolongs the life of the motor. The VSD also
improves power factor corrections which can result in significantly lower
electricity costs for the CSG proponents.

Electric Oil Lift Well Head

VSD
enable AC motors to deliver optimum torque while drawing approximately up to 50
percent of its rated operating current.SkillsTech Australia has partnered with SchneiderElectric
to provide introduction courses in VSDs as they apply to CSG sector and Well
Heads. Email: garry.hargreaves@tafe.qld.edu.au at SkillsTech Australia.